For a naive forecast of the anchovy catch in 1988, we just use the 1987 catch.
\[\hat{x}_{1988} = x_{1987}\] Which is the same as saying that we put 100% of the ‘weight’ on the most recent value and no weight on any value prior to that.
\[\hat{x}_{1988} = 1 \times x_{1987} + 0 \times x_{1986} + 0 \times x_{1985} + \dots\]